Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Line baking sheets with parchment paper or silicone mats.
In a mixing bowl, whisk together the 2 ½ cups of all-purpose flour, cornstarch, baking soda, and sea salt. Set aside.
2 ½ cups all-purpose flour, 2 teaspoons cornstarch, ½ teaspoon baking soda, ½ teaspoon sea salt
In another bowl, cream together the softened butter and 1 cup of brown sugar, sugar, until light and fluffy. Add the egg, egg yolk, and vanilla extract, and mix until well combined. Making sure to scape down the bowl.
2 sticks, 1 cup packed light brown sugar, ½ cup granulated sugar, 1 large egg, 1 egg yolk, 2 teaspoons vanilla extract
Gradually add the dry ingredient mixture to the wet ingredients, mixing until a cookie dough forms. Set aside the dough while you prepare the pecan topping. Do not overmix.
For the pecan topping, melt 5 tablespoons of unsalted butter in a saucepan over medium heat. Stir in ½ cup of dark brown sugar, maple syrup, chopped pecans, and a pinch of salt. Cook for a few minutes, stirring occasionally, until the mixture thickens slightly. Add heavy cream and vanilla and cook for an additional 1 minute. Remove from heat, and let it cool.
5 Tablespoons unsalted butter, ½ cup dark brown sugar, 1/4 cup maple syrup, 1 ½ cups chopped pecans, Pinch of salt, ¼ cup heavy cream, 1 teaspoon vanilla extract
Take 1 large ice cream scoop portions of the cookie dough (1/4 cup), and roll them into balls. Place them on the prepared baking sheets, leaving space between each cookie. Refrigerate overnight or freeze for 1-2 hours.
Once ready to bake, pop the cookies in the oven. Bake for 12-13 minutes or until the edges are golden brown.
Immediately take the back of a measure spoon, and press down the center of the cookie to create a little well.
Allow the cookies to cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.
Top with a a large tablespoon full of the pecan mixture, and sprinkle with flakey sea salt.